ContourPlot3D[x^3+y^2-z^2,{x,-2,2},{y,-2,2},{z,-2,2}]
ContourPlot3D[x^4+y^4+z^4-(x^2+y^2+z^2)^2+3*(x^2+y^2+z^2),{x,-2,2},{y,-2,2},{z,-2,2}]
